As described in Japan Laid-Open Patent Application Publication No. 2011-122640 or Japan Laid-Open Patent Application Publication No. JP-A-2009-250288, torque converters are often provided with a lock-up device for directly transmitting torque from a front cover to a turbine. The lock-up devices described in the PTLs include: a piston that can be frictionally coupled to the front cover; a retaining plate fixed to the piston; a plurality of torsion springs disposed on the outer peripheral side and the inner peripheral side in the radial direction; and a driven plate for transmitting torque transmitted thereto through the plural torsions springs to the turbine.
The outer peripheral side torsion springs and the inner peripheral side torsion springs are herein coupled by a pair of plates fixed to each other by rivets. Specifically, the inner peripheral side torsion springs are disposed between a first plate and a second plate, and are accommodated in spring accommodation portions formed in the both plates. Further, the circumferential ends of each spring accommodation portion can be engaged with the circumferential ends of each inner peripheral side torsion spring. Moreover, the outer peripheral part of the first plate is formed so as to be extending to the outer peripheral side torsion springs, and is engaged with the circumferential ends of the outer peripheral side torsion springs.
On the other hand, the outer peripheral end portion of the driven plate extends to the position between the first plate and the second plate, and has window holes formed for accommodating the inner peripheral side torsion springs. The inner peripheral part of the driven plate is fixed to the turbine.
The retaining plate is herein provided for transmitting torque from the piston to the outer peripheral side torsion springs. The retaining plate is fixed to the turbine-side lateral surface of the piston by rivets or the like. Further, the outer peripheral part of the retaining plate is partially bent towards the turbine, and the bent portions are engaged with the circumferential ends of the outer peripheral side torsion springs.
In such a lock-up device, torque is transmitted from the piston to the outer peripheral side torsion springs through the retaining plate, and is further transmitted to the inner peripheral side torsion springs through the first and second plates. Then, the torque transmitted to the inner peripheral side torsion springs is transmitted to the turbine through the driven plate.